Grays Landing Spillway and Stilling Basin, Monongahela River, Pennsylvania; Hydraulic Model Investigation.

Tests were conducted on a 136-scale section model to investigate the hydraulic performance of the deeply submerged stilling basin for the Grays Landing Spillway. The model was used to evaluate and develop the most satisfactory stilling basin for optimum hydraulic performance. The purpose of the model investigation also included determining the pressures along the spillway crest, velocities in the stilling basin and exit channel, and the capability of various stilling basins to pass ice without impacting and abrading the apron, baffle piers, and end sill. The size, gradation, and extent of riprap required for adequate protection of the downstream channel were also determined. The hydraulic model investigation of the stilling basin revealed the general adequacy of the design of the spillway with satisfactory performance of the proposed spillway crest. From the hydraulic performance of various types of energy dissipators investigated, the most appropriate stilling basin was the type 5 design. Shorter basins produced higher velocities downstream up to 15.5 fps and required larger downstream riprap protection. The type 5 design stilling basin allowed the baffle blocks to be located farther downstream to prevent the direct attack of ice against the baffles and stilling basin apron.